This invention relates to carburetor choke valve controls and, more particularly, to slowing down the rate of choke valve closing when an engine on which the carburetor is installed is shut off.
On newly designed four-cylinder engines, the engine block is typically cast iron while the engine's intake manifold and the carburetor mounted on the manifold are a lighter weight material such as aluminum. Carburetors for use on four-cylinder engines include a choke valve and fast idle cam arrangement and as the engine heats up, the choke valve is gradually opened. As this occurs, the fast idle cam moves from its top to its bottom step. When the engine is shut off, the carburetor and manifold cool down to ambient temperature faster than the engine because of the differences in mass between them. Because the carburetor cools to ambient temperature, the fast idle cam is returned to its top step when the engine is restarted. If this occurs before the engine cools to ambient temperature, the engine will be difficult to start and when it does, it will run at a higher rpm than is necessary. Further, the operator can do nothing to control the rpm at which the engine runs. Since the air-fuel mixture supplied the engine at this time is rich, HC and CO emission levels are high and because the engine is running at a faster than necessary rate, fuel economy suffers.